Resolving the Controversy over the Core Radius of 47 Tucanae (NGC 104)Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.Lick Observatory Bulletin 1395.

This paper investigates the discrepancy between recent measurements of the density profile of the globular cluster 47 Tuc that have used Hubble Space Telescopedata sets. A large core radius would support the long-held view that 47 Tuc is a relaxed cluster, while a small core radius may indicate that it is in a post-core-collapse phase or possibly even on the verge of core collapse, as suggested by a variety of unusual objects-millisecond pulsars, X-ray sources, high-velocity stars-observed in the core of the cluster. Guhathakurta et al. used pre-refurbishment Wide Field Planetary Camera 1 (WFPC1) V-band images to derive rcore= 23''± 2''. Calzetti et al. suggested that the density profile is instead a superposition of two King profiles, one with a small,8''core radius and the other with a 25''core radius, based on U-band Faint Object Camera (FOC) images. More recently, De Marchi et al. have used deep WFPC1 U-band images to derive rcore= 12''± 2''. The cluster centers used in these studies are in agreement with one another; differences in the adopted centers are not the cause of the discrepancy. Our independent analysis of the data used by De Marchi et al. reaches the following conclusions: